1. Field of the Invention
The present invention relates to a method of operating a pre-mixed burner at or above atmospheric pressure by blending a gaseous or liquid fuel and combustion air preferably together with a cooling fluid in a mixer and reacting the mixture so obtained in a downstream combustion chamber where a flame is formed, the temperature and thence the speed of said flame being relatively low under the given conditions.
2. Prior Art
It is well-known that the products of the combustion of gaseous or liquid fuel contain oxides of nitrogen (hereinafter referred to as "NO.sub.x ") which are undesirable, both because they contribute to air pollution and because they may affect a product or a charge which comes into contact with said products of combustion. As prior work has shown, said NO.sub.x is mainly formed by reactions of nitrogen compounds contained in the fuel and the reaction at high temperature of molecular nitrogen which is a constituent of the combustion air and may also be contained in certain fuels such as natural gas. The latter thermal formation of NO.sub.x is a reaction which proceeds at a particularly high rate above a very high limit temperature which is, for example, approximately 1,600.degree. C. for the combustion of natural gas.
European Patent Application No. EP-B00 21 035 reveals a method which allows the complete combustion of gaseous or vapourized fuel at a relatively low temperature, thereby producing a flue gas containing extremely little NO.sub.x and provides for flame stability over a very wide heat output range and more particularly at very high heat outputs. For such a very low NO.sub.x output and such high flame stability, said method proposes the utilization of a cooling fluid which reduces the flame temperature and nonetheless permits stable combustion, the flame formed during the combustion of the mixture being of a particular geometry and being shielded from extraneous gaseous fluids and extraneous temperature effects until the complete burnout of the mixture.